import {Matrix4, Mesh, MeshBasicMaterial} from '../../three.module.js';

/**
 * A shadow Mesh that follows a shadow-casting Mesh in the scene, but is confined to a single plane.
 */

const _shadowMatrix = new Matrix4();

class ShadowMesh extends Mesh {

  constructor(mesh) {

    const shadowMaterial = new MeshBasicMaterial({

      color: 0x000000,
      transparent: true,
      opacity: 0.6,
      depthWrite: false

    });

    super(mesh.geometry, shadowMaterial);

    this.meshMatrix = mesh.matrixWorld;

    this.frustumCulled = false;
    this.matrixAutoUpdate = false;

  }

  update(plane, lightPosition4D) {

    // based on https://www.opengl.org/archives/resources/features/StencilTalk/tsld021.htm

    const dot = plane.normal.x * lightPosition4D.x +
      plane.normal.y * lightPosition4D.y +
      plane.normal.z * lightPosition4D.z +
      -plane.constant * lightPosition4D.w;

    const sme = _shadowMatrix.elements;

    sme[0] = dot - lightPosition4D.x * plane.normal.x;
    sme[4] = -lightPosition4D.x * plane.normal.y;
    sme[8] = -lightPosition4D.x * plane.normal.z;
    sme[12] = -lightPosition4D.x * -plane.constant;

    sme[1] = -lightPosition4D.y * plane.normal.x;
    sme[5] = dot - lightPosition4D.y * plane.normal.y;
    sme[9] = -lightPosition4D.y * plane.normal.z;
    sme[13] = -lightPosition4D.y * -plane.constant;

    sme[2] = -lightPosition4D.z * plane.normal.x;
    sme[6] = -lightPosition4D.z * plane.normal.y;
    sme[10] = dot - lightPosition4D.z * plane.normal.z;
    sme[14] = -lightPosition4D.z * -plane.constant;

    sme[3] = -lightPosition4D.w * plane.normal.x;
    sme[7] = -lightPosition4D.w * plane.normal.y;
    sme[11] = -lightPosition4D.w * plane.normal.z;
    sme[15] = dot - lightPosition4D.w * -plane.constant;

    this.matrix.multiplyMatrices(_shadowMatrix, this.meshMatrix);

  }

}

ShadowMesh.prototype.isShadowMesh = true;

export {ShadowMesh};
